Gap junction-mediated intercellular ionic and metabolic coupling provides both homeostatic and signaling functions among astrocytes throughout the brain, and CNS pathology both results in and is caused by disruptions in astrocyte gap junction signaling. It is now well known that gap junction proteins (connexins) interact with other proteins, forming a molecular complex we term the Nexus. Recent data indicate that Nexus is a highly dynamic signaling unit, where direct linkages of connexins to adaptor and scaffolding molecules are bound to cytoskeletal, cytoplasmic and other membrane proteins, polarizing the astrocyte. The overall goal of this grant proposal is to understand how gap junctions in astrocytes control organization of this endfoot complex and thus control blood-brain-barrier integrity. To accomplish this goal, we propose to: Aim 1: Test the hypothesis that localization and mobility of gap junction proteins and their binding partners determines organization of astrocyte endfeet. Aim 2. Determine downstream effects of connexins on endothelial tight junction formation. Aim 3. Validate the hypothesis that localization and mobility of gap junction proteins and their binding partners determines organization of astrocyte endfeet using mice with modified connexin expression We believe that these interdisciplinary and innovative studies will provide the first molecular insights into the role of the astrocyte Nexus i establishment of cell polarity and thus identify important astrocyte functions that can be targeted to reverse disorders of astrocyte polarity.